1. Field of the Invention
This invention relates to a pressure reduction apparatus for solid particle-containing high pressure liquids and, more particularly, a pressure reduction apparatus for use in chemical plants which deal with high pressure liquids comprising solid particles such as solutions of coal liquefaction products from coal liquefaction plants.
2. Description of the Prior Art
A variety of chemical plants utilizing a process of reducing the pressure of high pressure liquids containing solid particles are known. Typical of such plants are coal liquefaction plants which have been recently reperceived accompanied by worsening of the condition of petroleum supply. In coal liquefaction plants, coal is pulverized and dehydrated, after which suitable solvents are added to the coal pieces to form a slurry. The slurry is pressurized and pre-heated, and is subjected to liquefaction by hydrogenation reaction. The resulting high temperature and high pressure coal liquefaction solution product is subjected to the gas-liquid separation, followed by pressure reduction. Then, the heavy and light oil products are fractionally distilled as they are or after further gas-liquid separation. For pressure reduction of the solution of coal liquefaction product, it is the usual practice to make use of the throttling effect of a flow regulator valve and is usually referred to as a let-down valve. However, a member of the valve which contacts with the solution tends to be considerably damaged by solid particles of organic matter contained in the solution. In view of the above fact, there has been proposed, for example, in Japanese Patent Application No. 56-108365, an apparatus in which pressure energy is recovered simultaneously with the pressure reduction of the high pressure liquid or solution. In this energy recovery apparatus, the solution of coal liquefaction product is fed to a cylinder in which the pressure energy is converted into and recovered as mechanical energy. The solution which has been reduced in pressure by the conversion is fed to a subsequent step by the use of mechanical energy from other cylinders. However, the mechanical motion in the energy converter involves problems such as abrasion or erosion of and a thermal influence on sliding portions and valves which contact with the solution.